The copper mould tube is the core component of the continuous casting machine, directly in contact with high-temperature molten steel. Its main function is to rapidly cool and solidify the molten steel into a solid shell of a certain thickness and shape, providing the initial shape and size, such as square billets, rectangular billets, and round billets, for the cast billet.

It is usually made of high thermal conductivity copper alloys, such as phosphorus-deoxidized copper (TP2), silver-copper (CuAg0.1), or chromium-zirconium-copper (Cr-Zr-Cu), to enhance high-temperature strength, wear resistance, and creep resistance.

The blackening of copper tubes in steel plant moulds may be caused by multiple factors, including oxidation, corrosion, and sedimentation. To prolong the service life of copper tubes, regular maintenance and upkeep are necessary. Steel plants can also use cleaner water to clean the moulds, which helps reduce oxidation and sediment buildup, lowering the likelihood of the copper tubes turning black.